Simultaneous determination of the diuretics triamterene and furosemide in pharmaceutical formulations and urine by HPLC-EC

A high performance liquid chromatographic method with amperometric detection has been developed for the simultaneous determination of two diuretics: triamterene and furosemide, using a mu-Bondapak C-18 column. The mobile phase consisted of a mixture water:acetonitrile, 30:70, 5mM in KH2PO4/K2HPO4, pH 5.5 pumped at a flow rate of 1 mL/min. The amperometric detector, equipped with a glassy carbon electrode, was operated at +1300 mV. The method was applied to the determination of both diuretics in the pharmaceutical formulation Salidur (triamterene 25 mg and furosemide-xanthinol 77.6 mg) and real urine samples obtained from a healthy volunteer after the ingestion of a single dose of Salidur. Using a simple liquid-liquid extraction procedure, good recovery and separation from interferences found in urine matrix is achieved and the simultaneous determination of both compounds is possible. Reproducibility is good with relative standard deviations lower than 1.5% intra-day and 5% inter-day and the method is accurate since errors obtained for tablets are lower than 1%. The determination limits are 15 ng/mL for furosemide and 0.1 ng/mL for triamterene. Results obtained from urine samples are in accordance with those expected from pharmacokinetic studies.